1. Field of the Invention
This invention relates to tools used in the drilling and servicing of oil and gas wells, referred to hereinafter as “wells.” More particularly, this invention generally relates to a downhole (that is, to be run from the surface down into a well) tool comprising interchangeable service components, which are retained on the outer diameter of a central mandrel. The invention can be used to clean the inner walls of casing, risers (e.g. on a floating drilling rig), or any like surfaces, or to collect solid contaminants generally present in these sections either on inner walls, or within the wellbore fluid itself. The interchangeable components are interchangeable in various configurations, and mounted on the mandrel so as to be either rotational or non-rotational with respect to the mandrel. It is to be understood that “well servicing apparatus” refers to apparatus to service not only the physical structure of the well (or “wellbore”) (namely, the casing string forming the wellbore, a riser associated with a floating rig, or any other downhole tubular), but also the fluids contained within the wellbore.
2. Related Art
While the present invention can be used in a variety of applications, for exemplary purposes the invention will be described in connection with the cleaning of casing or riser walls after a well has been drilled and a clear completion fluid is put into the well. It is after a well has been drilled and a clear completion fluid is put into the well. It is understood that the present invention can be used to clean any sort of downhole tubular, including risers, BOP stacks, casing strings, etc.
Oil and gas wells are usually drilled with a solids-laden fluid in the borehole, said fluid commonly referred to as drilling “mud.” Mud provides several essential purposes, including control of formation pressure, cooling of the drillbit, removal of drill cuttings from the borehole, etc.
However, after the well is drilled and production casing is run, in many well completion scenarios (for example, gravel packed completions), the drilling mud must be displaced from the wellbore and a clear (that is, solids-free) fluid, known as a completion fluid or completion brine, circulated into the wellbore. The use of solids-free completion fluids is necessary in order to gravel pack the completion interval. However, even though the completion fluid (when put into the wellbore) is substantially free of solids, it can be appreciated that the wellbore tends to retain a quantity of drilling mud and other solids on the inner wall of the casing or riser. In addition to simply circulating the completion fluid into and out of the wellbore, it is usually necessary to mechanically remove the layer of mud, usually by scraping with some downhole tool. Also, it is common that pieces of ferrous and non-ferrous “junk” remain in the wellbore, which must preferably be removed.
Over the years, a number of tools have been developed for this task, for example casing scrapers and brushes for cleaning the tubular (whether it be casing, a riser, etc.) wall; junk baskets for removing certain undesired objects from the wellbore; and downhole magnets for removing ferrous objects. Traditionally, each of such tools are separate, dedicated tools (that is, separate casing scrapers/brushes, junk baskets, and magnets), with little or no common structural elements. As a result, the known prior art tools have certain limitations, including high cost, difficulty in changing scraper blades/brushes, etc.
It is desired to have a downhole well servicing apparatus which provides a central carrier or mandrel to which can be easily and removably mounted a variety of well service components, including brushes, junk baskets, and magnets, in addition to stabilizer elements to mount the other various servicing tools in proper position on the central mandrel. It is further desired to have an apparatus comprising certain removable and replaceable elements which minimize wear on the central mandrel, which is generally the most expensive component of the apparatus.